Optically active carboxylic acid derivatives and liquid crystalline compositions comprising them

ABSTRACT

An optically active carboxylic acid derivative represented by the general formula ##STR1## wherein R represents a normal alkyl group having 1 to 20 carbon atoms, m and n represent 0 or 1 but are not 1 at the same time, X represents a hydrogen or halogen atom, Y represents a hydrogen or fluorine atom, provided that when Y is a hydrogen atom, X is a halogen atom, and that when n is 0, Y is ahydrogen atom, and Q* represents an optically active alkyl or 1-alkoxyethyl group having an asymmetric carbon atom.

This invention relates to an optically active carboxylic acid derivativeand a liquid crystalline composition comprising it. More specifically,this invention relates to a compound which is useful as a ferroelectricliquid crystalline material and specifically has a wider effectivetemperature range and better response than conventional ferroelectricliquid crystalline materials, and to a liquid crystalline compositionwhich comprises the above compound and has a high practical value as aliquid crystal display element.

Liquid crystal display elements now find widespread use because of theirvarious superior characteristics. For example, they are operable at lowvoltages and with a small amount of power consumption, and enable thindisplay. Moreover, since they are of light-receiving type, they can beused in bright places without burden on eyes. Presently, the most commondisplay mode is a twisted nematic (TN) mode. The TN display mode uses anematic liquid crystal which has all of the aforesaid characteristicsbut is quite slow in speed of response as compared with other lightemission type display modes including CRT. Moreover, since breaking ofan applied electric field returns the display to the original state, adisplay memory (memory effect) cannot be obtained. For this reason, muchrestriction is imposed on application of the TN display mode to a lightshutter, a printer head, a TV screen, etc.

In addition to the TN mode, a guest-host (GH) mode, an electricallycontrolled birefringernce (ECB)) mode, a phase change (PC) mode and athermoelectric mode have been studied and developed for use in liquidcrystal display elements having their own unique characteristics. They,however, do not show any particular improvement over the TN mode inrespect of response characteristics. On the other hand, a dual-sequenceaddress field mode and a super TN mode have been developed as liquidcrystal display modes allowing high-speed response. These display modesshow a considerable improvement in response, but still do not prove tobe entirely satisfactory. In addition, the dual sequence address fieldmode has the defect that its operating circuit becomes too complex. Thesuper TN mode is unsuitable for color display because the screen turnsyellow. Attempts have therefore been made to develop new liquid crystaldisplay modes having better response characteristics.

Ferroelectric liquid crystals were recently reported [R. Mayer et al.,J. Physique, 36, L69 (1975)] as liquid crystals which meet the abovepurpose. It was pointed out that display elements utilizing theferroelectric liquid crystals permit response at high speeds 100 to 1000times the speeds of the conventional liquid crystal display elements andhave a memory effect attributed to bistability [N. A. Clark, S. T.Lagerwall, Appl. Phys. Lett., 36, 899 (1980)]. These display elementsare expected to be applied to many display elements in various fields,for example in a TV screen, a high-speed light shutter, a printer head,computer terminals, and the like.

The ferroelectric liquid crystals are those having liquid crystallinephases belonging to tilt-type chiral smectic phases. For practicalpurposes, a chiral smectic C (hereinafter abbreviated as "S_(C) *")phase having the lowest viscosity is most desirable. Liquid crystallinecompounds having S_(C) * phase have been so far studied and many suchcompounds have already been known.

Typical examples are Schiff base liquid crystals of (s)-2-methylbutylp-decyloxybenzylideneaminocinnamate (abbreviated as "DOBAMBC") and itsanalogs. DOBAMBC is now one of the most frequently used liquidcrystalline compounds for studying the properties and alignment offerroelectric liquid crystals and represents one standard of theimportant properties of ferroelectric liquid crystals, such as a helicalpitch value, spontaneous polarization, etc. However, DOBAMBC andcompounds of its series are not satisfactory for practical applicationbecause of one or more drawbacks: (1) they lack light stability; (2)they lack stability to water; (3) they themselves are colored; and (4)the temperature range in which the above compounds enantiotropicallyshown a S_(C) * phase is narrow and within 20° C. and remote from theroom temperature range [(1) P. Keller et al., J. de Physique, 37, C3(1976); (2) ibid, Acad. Sc. Paris, 282, C639 (1976); (3) B. I.Ostrouskii et al., Ferroelectrics, 24, 309 (1980); (4) K. Yoshino etal., Japanese J. of Appl. Physics, 23, L175 (1984); and (5) Isogai etal., Japanese Laid-Open Patent Publication No. 59-98051].

Some azoxy liquid crystals have been known, but they are not suitablefor practical use owing to their strong coloration [P. Keller et al.,Ann. Phys. 3, 139 (1978)]. To remedy this defect, chemically stableester-type liquid crystalline compounds have recently been studies, andmany reports have already been made.

Reviews introducing a great deal of these compounds are (1) J. W. Goodbyet al., Liquid Crystals and Ordered Fluids, vol. 4, pp. 1-32, (2) J. W.Goodby, T. M. Leslie, Mol. Cryst. Liq. Cryst., 110, 175 (1984). M.Isogai et al., EP-0110299 may also be cited as a documents describingmany such compounds.

As described in the above-cited literature references, ferroelectricityin liquid crystals occurs when the liquid crystals have the tilt-typechiral smectic phases, more specifically a chiral smectic C phaseS_(C) * phase), a chiral smectic F phase (S_(F) * phase), a chiralsmectic I phase (S_(I) * phase), a chiral smectic H phase (S_(H) *phase), a chiral smectic G phase (S_(G) * phase), a chiral smectic Jphase (S_(J) * phase) and a chiral smectic K phase (S_(K) * phase), andit is said that the S_(C) * phase is most practical. In order for aliquid crystalline compound to have the S_(C) * phase or another chiralsmectic phase, it must be a chiral compound. The chiral compound may beobtained by introducing a group having an asymmetric carbon atom, i.e.,an optically active group, into the compound.

High-speed response is one characteristic of a ferroelectric liquidcrystal. The response time (τ) is approximately represented by thefollowing equation

    τ=k·η/Ps                                  (A)

wherein η is the viscosity of the liquid crystals, Ps is spontaneouspolarization and k is a proportional constant. Hence, with increasingPs, the response time decreases and the effectiveness of theferroelectric liquid crystals appears to an increasing extent.

A widely known liquid crystalline compound called DOBAMBC for short issaid to have a spontaneous polarization of about 4 nC (nonacoulomb)/cm²,and many other known compounds have a spontaneous polarization in therange of 1 to 10 nC/cm².

In order for ferroelectric liquid crystals to be useful as displayelements in practical applications, they are first required to show anS_(C) * phase over a wide temperature range including room temperature.For this purpose, it is the general practice to mix two or moreferroelectric compounds so that the melting points are lowered and theresulting mixture shows a S_(C) * phase over a wide temperature range.Generally, a ferroelectric liquid crystal showing a S_(C) * phase has ahigher viscosity than a smectic C liquid crystal having no asymmetriccarbon atom. Accordingly, in practice, there has previously been used atechnique by which in order to lower the viscosity of the liquidcrystal, a ferroelectric S_(C) * composition is prepared by adding acompound or composition showing a S_(C) * phase, or having an asymmetriccarbon atom but not showing the S_(C) * phase, to a smectic C liquidcrystal or its composition. It is not particularly important, thereforeto obtain a liquid crystalline composition by mixing ferroelectricliquid crystalline compounds with each other, but this further increasesan effect of obtaining high-speed response and a broad S_(C) * phasetemperature range.

It is an object of this invention to provide a novel liquid crystallinecompound which can assume a ferroelectric liquid crystalline phase,particularly a ferroelectric chiral smectic C phase, over a widetemperature range.

Another object of this invention is to provide a liquid crystal having ahigh-speed response using such a liquid crystalline compound or acomposition comprising it.

According to this invention, there is provided a liquid crystallinecomposition comprising at least one optically active carboxylic acidderivative represented by the general formula ##STR2## wherein Rrepresents a linear alkyl group having 1 to 20 carbon atoms, m and nrepresent 0 or 1 but are not 1 at the same time, X represents a hydrogenor halogen atom and Y represents a hydrogen or fluorine atom providedthat when Y is a hydrogen atom, X is a fluorine atom and when n is 0, Yis a hydrogen atom, and Q* represents an optically active alkyl or1-alkoxyethyl group having an asymmetric carbon atom, or a combinationof at least one said compound of formula (I) with at least one othercompound.

The present inventors, in the course of developing various liquidcrystalline compounds, found that a group of the compounds of generalformula (I) are a new group of ferroelectric smectic liquid crystallinecompounds having properties not seen in the prior art.

In the ferroelectric smectic liquid crystals so far disclosed, theoptically active moiety is an ester linkage derived from the opticallyactive alcohols used as raw materials, an ether linkage, or an opticallyactive alkyl group directly bonded to the central ring portion. Thecompounds of formula (I) in accordance with this invention are differentfrom these known compounds and are characterized first of all by thefact that the optically active moiety is a group derived from theoptically active carboxylic acid.

There are a few examples of liquid crystalline compounds synthesizedfrom optically active carboxylic acids. Japanese Laid-Open PatentPublication No. 218358/1985 discloses liquid crystalline compoundsproduced by using halogenated optically active carboxylic acidderivatives. These compounds are greatly different in basic skeletonfrom the compounds (I) of this invention and have a narrower S_(C) *phase temperature range. Furthermore, since they are secondary halides,they are unstable and are considered to lack practical utility. JapaneseLaid-Open Patent Publication No. 90290/1985 shows in its claim compoundsrepresented by the following general formula ##STR3## wherein Rrepresents an alkoxy or alkyl group, m and n are 1 or 2, X represents acarbonyloxy group, an oxycarbonyl group, etc., and Y represents analkoxy carbonyl group, an alkoxy group, an alkanoyl group, analkanoyloxy group, etc.

Its specification, however, quite fails to give any description of amethod of production or physical property values of compounds of theabove formula in which Y is an alkanoyloxy group (namely, whereoptically active carboxylic acids are used as starting materials).

As outlined above, the utilization of optically active carboxylic acidsis still not general, and much is unknown of the properties of liquidcrystals prepared therefrom. As will be stated hereinafter, whenoptically active carboxylic acids are utilized in accordance with thisinvention, many compounds can be prepared which have a greaterspontaneous polarization than in the case of utilizing conventionaloptically active 2-methylbutanol esters. This fact was unexpectedlydiscovered by the present inventors.

The second characteristic feature of the compounds (I) of this inventionis that they are chemically stable since they have halogen-substitutedaromatic esters as their central skeleton.

As shown in EP Publication No. 188222, halogen-substituted compoundsbring about various advantages over non-substituted compounds. Forexample, the halogen-substituted compounds tend to show a S_(C) * phaseover a broader temperature range, and have a stronger tendency to failto show other smectic phases at temperatures lower than the temperaturesat which they show a S_(C) * phase. Furthermore, when they are mixed asa composition, a larger fall in melting point can be expected. Thesefactors are very important in practical application because if in theproduction of a composition by mixing two or more compounds in order tolower the melting points, these compounds have other smectic phases attemperatures lower than the temperatures at which they show a S_(C) *phase, the resulting composition is liable to have undesirable othersmectic phases.

The effectiveness of halogen substitution is shown specifically belowwith respect to the compounds (I).

(1) with regard to a group of compounds of the following formula##STR4## which corresponds to formula (I) in which m=0, n=1, Y=H and##STR5## those of the above formula in which X is H show other smecticphases at temperatures lower than the temperatures at which they show aS_(C) * phase, whereas those of the above formula in which X is F showonly a crystalline phase at temperatures lower than the temperatures atwhich they show a S_(C) * phase.

(2) With regard to a group of compounds of the following formula##STR6## which corresponds to general formula (I) in which R=C₁₂ H₂₅,m=0, n=1, Y=H ##STR7## those of the above formula in which X is Cl havethe lowest melting point, and those of the above formula in which X is Fhave the next lowest melting point. Those of the above formula in whichX is H have the highest melting point. The fluorine-substitutedcompounds have the broadest temperature ranges in which they show aS_(C) * phase.

Another characteristic of the compounds (I) is that among a group ofcompounds having three phenyl nuclei (tricyclic), those in which theasymmetric carbon atom Q* is vicinal to the carbonyl group do not easilyassume other smectic phases at temperatures lower than the temperaturesat which they show a S_(C) * phase, and that those having a fluorinesubstituent at the biphenyl ring, with a few exceptions, do not assumeother smectic phases at temperatures lower than the temperatures atwhich they show a S_(C) * phase.

While DOBAMBC has a spontaneous polarization of about 4 nC/cm², thecompounds (I) of this invention have a spontaneous polarization of (1) 1to 4 nC/cm² when Q* is 2-methylbutyl, (2) 3 to 7 nC/cm² when Q* is1-methylpropyll, and (3) 60 to 130 nC/cm² when Q* is 1-alkoxyethyl. Thespontaneous polarization value depends upon the distance between theasymmetric carbon and the permanent dipole existing in a directionperpendicular to the long axis of the molecules of the compound (I).Particularly, the compounds corresponding to (3) have a very largespontaneous polarization because the asymmetric carbon is interposedbetween two permanent dipoles.

The compounds of general formula (I) are hydroquinone derivatives when mand n are both zero, and biphenol derivatives when n is 1. Thesehydroquinone and biphenol derivatives readily show a chiral nematicphase (generally called a cholesteric phase) at temperatures higher thanthe temperatures at which they show a S_(C) * phase. The existence of achiral nematic phase is very important in filling a liquid crystallinecompound or a liquid crystalline composition in a liquid crystal celland uniformly aligning its layers. In the absence of the chiral nematicphase, it is considered as difficult by the present-day technology toobtain uniform alignment after filling the compound or composition intothe liquid crystal cell. From this standpoint, the compounds (I) of thisinvention have a great advantage.

The compound of the general formula (I) can be produced byesterification reaction between a compound represented by the generalformula ##STR8## wherein R₁ represents a linear alkyl group having 1 to20 carbon atom, X represents a hydrogen or halogen atom, and mrepresents 0 or 1, and a compound represented by the general formula##STR9## wherein Y represents a hydrogen or fluorine atom, n represents0 or 1, and Q* represents an optically active alkyl or 1-alkoxyethylgroup, provided that when n is 0, Y is a hydrogen atom, for example bycondensation reaction using N,N'-dicyclohexylcarbodiimide, and moregenerally condensing an acid halide corresponding to the compound ofgeneral formula (II) with the compound of general formula (III).

The compound of general formula (II) is a 4-alkoxybenzoic acidderivative when m is 0, and a 4'-alkoxybiphenyl-4-carboxylic acid when mis 1. Compounds of the above formula in which X is a hydrogen atom canbe obtained by general etherification by condensation betweencommercially available 4-hydroxybenzoic acid or4-hydroxybiphenyl-4-carboxylic acid and an alkyl halide. Compounds ofthe above formula in which X is a halogen atom and m is 0(4-hydroxy-halogenobenzoic acids) can be produced by the Friedel-Craftsacylation of 2-halogenoanisoles or 3-halogenoanisoles using acetylchloride, followed by oxidation with a sodium hypobromite solution, anddemethylation with 48% aqueous hydrogen bromide solution, or bybromination of 2-halogenoanisoles, followed by Grignard reagentsynthesis, carboxylation by reaction with carbon dioxide, anddemethylation with a 48% aqueous hydrogen bromide solution. This seriesof steps is schematically shown below (the symbols used in this schemehave conventional meanings, and are independent from those used in thegeneral formulae hereinabove. ##STR10##

Compounds of formula (II) in which m is 1 and X is a halogen atom(4-hydroxyhalogenobiphenyl-4-carboxylic acids) can be produced bybromination of halogenoanisoles, Grignard reagent synthesis and Grignardcoupling reaction with iodobenzene in the presence of palladiumchloride, and thereafter reacting the resulting4-methoxyhalogenobiphenyls in the same way as in the above production of4-hydroxyhalogenobenzoic acids. This series of steps is schematicallyshown below (the symbols used in this scheme have conventional meanings,and are independent from those used in the general formulaehereinabove). ##STR11##

The compounds of general formula (III) can be produced by estercondensation reaction between a compound represented by the generalformula ##STR12## wherein Y represents a hydrogen or fluorine atom, nrepresents 0 or 1, provided that when n is 0, Y represents a hydrogenatom with a compound represented by the general formula

    Q*-COOH                                                    (V)

wherein Q* represents an optically active alkyl or 1-alkoxyethyl group.This ester condensation reaction can be carried out by quite the sameprocedure as used in the ester condensation reaction between thecompound of general formula (II) and the compound of general formula(III).

The compound of general formula (IV) is hydroquinone when n is 0 (i.e.,Y=H) and 3,3'-difluoro-4,4'-biphenol when n is 1 and Y is F.3,3'-Difluoro-4,4'-biphenol can be produced by bromination of2-fluoroanisole, followed by Grignard reagent synthesis and couplingreaction with 2-fluoro-4-bromoanisole.

The optically active carboxylic acid of general formula (V) can beproduced by the oxidation of the corresponding optically active primaryalcohol with potassium permanganate, or by Grignard reagent synthesis ofan optically active alkyl halide followed by carboxylation with carbondioxide gas. As a specific example, an optically active2-alkoxypropionic acid can be produced by etherifiying optically activeethyl lactate with an alkyl iodide in the presence of silver oxide andhydrolyzing the resulting optically active ethyl 2-alkoxypropionate withan alkali. The process of producing the optically active2-alkoxypropionic acid is shown by the following scheme (the symbolsused in this scheme have conventional meanings, and are independent fromthose used in the general formulae hereinabove). ##STR13##

The following Examples and Comparative Examples illustrate the presentinvention more specifically. It should be understood that the spirit andscope of the present invention are not limited by these examples.

EXAMPLE 1

Synthesis of 4-[(s)-2-methylbutylcarbonyloxy]phenyl4"-decyloxy-3"-fluorobiphenyl-4'-carboxylate of general formula (I) inwhich R=n-C₁₀ H₂₁, X=F, m=1, n=0 and Q*=2-methylbutyl; compound No. S-1)

[1-1] Synthesis of 3'-fluoro-4'-hydroxybiphenyl-4-carboxylic acid

A 500 ml five-necked flask equipped with a stirrer, a condenser, anitrogen gas introducing tube, a thermometer and a dropping funnel andadapted to permit releasing of nitrogen gas from the top of thecondenser was charged with 2.5 g of flaky metallic magnesium and 120 mlof tetrahydrofuran (dried over sodium metal). A solution of 20.5 g of3-fluoro-4-methoxybromobenzene in 50 g of dry tetrahydrofuran was fedinto the dropping funnel. In a stream of nitrogen gas, the flask washeated while adding dropwise 3-fluoro-4-methoxybromobenzene little bylittle from the dropping funnel. With gradual reaction, the3-fluoro-4-methoxybromobenzene was added dropwise over the course of 30minutes. When the reaction proceeded during the dropwise addition, noexternal supply of heat is required because the reaction was exothermic.After the addition, the mixture was heated under reflux for 1 hour toproduce 3-fluoro-4-methoxyphenyl magnesium bromide. Then, to a flaskcharged with 20.3 g of iodobenzene, 0.20 g of palladium chloride and 100ml of dry tetrahydrofuran was added dropwise to the abovetetrahydrofuran solution of 3-fluoro-4-methoxyphenyl magnesium bromidewhile the iodobenzene solution was stirred. The addition was carried outover the course of 40 minutes, and the mixture was heated under refluxfor 2 hours. Then, the temperature of the reaction mixture was returnedto room temperature and 10% hydrochloric acid was added. The mixture wasstirred and after adding hexane, further stirred sufficiently. Theorganic layer was separated, washed with water, and concentrated. Fromthe residue, 3-fluoro-4-methoxybiphenyl was separated by silica gelcolumn chromatography. The amount yielded 11.2 g; yield 55%.

Then, 11.2 g of the resulting 3-fluoro-4-methoxybiphenyl was fed into areaction flask equipped with a cooling tube together with 4.3 g ofacetyl chloride and 100 ml of carbon disulfide. An anhydrous calciumtube was attached to the upper portion of the flask to shut off water.While the flask was cooled with ice, 9.0 g of anhydrous aluminumchloride was added. The mixture was stirred for 2 hours, and then gentlyheated under reflux for 5 hours.

After the reaction, the reaction mixture was poured into a large amountof 10% hydrochloric acid, and the mixture was fully stirred. Theresulting precipitate (9.1 g) was collected by filtration, andrecrystallized from isopropyl alcohol to give 7.2 g (yield 53%) of4-acetyl-3'-fluoro-4'-methoxybiphenyl.

The resulting 4-acetyl-3'-fluoro-4'-methoxybiphenyl (7.2 g) wasdissolved in 300 ml of dioxane, and 360 ml of a solution of sodiumhypobromite (prepared from 75 g of sodium hydroxide and 78 g of bromine)was added over about 40 minutes at 0° to 5° C., and the mixture wasstirred at 30° to 35° C. for 2 hours. The excess of sodium hypobromitewas decomposed with a saturated aqueous solution of sodium hydrogensulfite, and 10% hydrochloric acid was added to adjust the pH of thesolution to 3 to 4. The solution was left to stand at 10° C. for 20hours to permit crystallization. The resulting crystals were filtered togive 7.2 g of 3'-fluoro-4'-methoxybiphenyl-4-carboxylic acid.Recrystallization from isopropyl alcohol gave 6.8 g of the desiredproduct. Yield 94%.

Subsequently, 6.8 g of 3'-fluoro-4'-methoxybiphenyl-4-carboxylic acidwas heated under reflux for 14 hours in 150 ml of 48% hydrobromic acidand 80 ml of dioxane. The volatile components were removed byevaporator, and the residue was washed several times with water to give6.10 g (yield 95%) of the desired3'-fluoro-4'-hydroxybiphenyl-4-carboxylic acid.

[1-2] Synthesis of 4'-decyloxy-3'-fluorobiphenyl-4-carboxylic acid

The resulting 3'-fluoro-4'-hydroxybiphenyl-'-carboxylic acid was heatedunder reflux for 10 hours in hydrous ethanol together with 1.2 moles,per mole of the carboxylic acid, of decyl bromide and 1.95 moles, permole of the carboxylic acid, of sodium hydroxide. Then, 10% hydrochloricacid was added to adjust the pH of the solution to 2 to 3. The solutionwas then heated under reflux for one hour. After cooling, the organicmaterials were extracted with chloroform. The chloroform layer waswashed with water and dried over anhydrous sodium sulfate. Thechloroform layer was concentrated to obtain crude crystals.Recrystallization from ethanol gave the desired4'-decyloxy-3'-fluorobiphenyl-4-carboxylic acid. The yield in thisalkoxylation reaction slightly varies depending upon the type of thealkyl bromide used, but is is generally 60 to 80%.

[1-3] Synthesis of 4-hydroxyphenyl (s)-3-methylpentanoate

Magnesium flask (2.5 g) and 10 ml of dry tetrahydrofuran were put in a300 ml flask, and heated under a nitrogen stream, and then a solution of15.1 g of (s)-2-methylbutyl bromide in 80 ml of tetrahydrofuran wasgradually added to prepare a Grignard reagent. Dry tetrahydrofuran (80ml) was added further, and carbon dioxide gas was blown into the mixtureat room temperature, and the reaction was carried out for 2 hours at areaction temperature of 40° to 60° C. After the reaction was ceased,dilute hydrochloric acid was added, and the mixture was diluted withether. The organic layer was separated, washed with water, dried overanhydrous magnesium sulfate, and concentrated to give 10.1 g (yield87.0%) of (s)-3-methyl pentanoic acid.

Subsequently, 10.1 g of (s)-3-methylpentanoic acid was stirred togetherwith 20 g of thionyl chloride at 15° to 20° C. for 10 hours. The excessof thionyl chloride was evaporated, and the residue was added to asolution of 22 g of hydroquinone in 100 ml of dry pyridine, and themixture was stirred at room temperature for 24 hours. After thereaction, pyridine was evaporated under reduced pressure. The residuewas dissolved in ethyl acetate, and repeatedly washed with waterthoroughly. The ethyl acetate layer was concentrated, and the desired4-hydroxyphenyl (s)-3-methylpentanoate was obtained in an amount of 12.0g (yield 66%).

[1-4] Synthesis of 4-[(s)-2-methylbutylcarbonyloxy]phenyl4"-decyloxy-3"-fluorobiphenyl-4'-carboxylate

Thionyl chloride (8.5 g) was added to 3.72 g of3'-fluoro-4'-decyloxybiphenyl-4-carboxylic acid, and one drop ofpyridine was added. The mixture was heated under reflux for 6 hours. Thevolatile components were evaporated under reduced pressure, and 20 g ofdry pyridine and 2.06 g of 4-hydroxyphenyl (s)-3-methylpentanoate wereadded. The mixture was stirred at room temperature for 20 hours. Afterthe reaction, the reaction mixture was poured into a large amount ofethyl acetate, and washed with dilute hydrochloric acid three times andsubsequently with water three times. The ethyl acetate layer was driedover anhydrous sodium sulfate, and concentrated to give 5.1 g of aresidue. The residue was purified by silica gel column chromatography(hexane/ethyl acetate eluent). Recrystallization from ethanol gave 3.60g (yield 64%) of the desired product.

Nuclear magnetic resonance spectrum [NMR for short), (CDCl₃, δ value,(proton)]: 0.80-2.25 (28H); 2.43-2.72 (2H) multiplet; 4.00-4.15 (2H)triplet; 7.01-8.30 (11H).

Infrared absorption spectrum (IR for short) (cm⁻¹):

Main absorptions: 2930, 2850, 1750, 1730, 1610, 1515, 1285, 1190, 1090,815, 765.

Mass spectrum: M/e=562 (C.I. method)

Phase transition temperature: N*-I point=-171.8° C.; S_(A) -N*point=168.5° C.; S_(C) *-S_(A) point=153.6° C.; m.p.=80.2° C.

EXAMPLE 2 Synthesis of 4-[(s)-1-methylpropylcarbonyloxy]-phenyl4"-dodecyloxy-3"-fluorobiphenyl-4'-carboxylate of general formula (I) inwhich R=n-C₁₂ H₂₅, X=F, m=1, n=0 and Q*-1-methylpropyl; compound No.S-2) [2-1] Synthesis of 4-hydroxyphenyl (s)-2-methylbutyrate

To a flask 10.2 g of (s)-2-methylbutanoic acid and 30 g of thionylchloride were added and stirred at room temperature for 30 hours. Then,thionyl chloride was evaporated, and the residue was added to 60 ml of asolution of 25.0 g of hydroquinone in dry pyridine. The mixture wasstirred at room temperature for 24 hours. Then, pyridine was evaporatedunder reduced pressure, and the residue was dissolved in ethyl acetateand fully washed with water repeatedly. The ethyl acetate layer wasconcentrated. The residue was purified by silica gel columnchromatography. 12.1 g (yield 62%) of the desired product was obtainedfrom the main fraction.

[2-2] Synthesis of 4-[(s)-1-methylpropylcarbonyloxy]phenyl4'-dodecyloxy-3"-fluorobiphenyl-4'-carboxylate

In the same was as described in paragraph [1-4] above, the desiredproduct was obtained in a yield of 69% from 4.0 g of4'-dodecyloxy-3'-fluorobiphenyl-4-carboxylic acid and 2.01 g of4-hydroxyphenyl (s)-2-methylbutyrate.

NMR (CDCl₃, δ, (proton): 0.80-1.95 (23H); 2.50-2.83 (1H) multiplet;4.00-4.15 (2H) triplet; 7.03-8.30 (11H).

IR (cm⁻¹), main absorptions: 2930, 2860, 1750, 1730, 1610, 1515, 1285,1190, 1090, 815, 715.

Mass spectrum: M/e=576 (C.I. method).

Phase transition temperatures: S_(A) -I point=161.0° C.; S_(C) *-S_(A)point=144.3° C.; m.p.=85.9° C.

In the same was as in Examples 1 and 2, the following compounds weresynthesized.

4-[(s)-2-Methylbutylcarbonyloxy]phenyl4"-octyloxy-3"-fluorobiphenyl-4'-carboxylate (compound No. S-3),

4-[(s)-2-Methylbutylcarbonyloxy]phenyl4"-dodecyloxy-3"-fluorobiphenyl-4'-carboxylate (compound No. S-4),

4-[(s)-2-Methylbutylcarbonyloxy]phenyl4"-tetradecyloxy-3"-fluorobiphenyl-4'-carboxylate (compound No. S-5),

4-[(s)-1-Methylpropylcarbonyloxy]phenyl4"-decyloxy-3-fluorobiphenyl-4'-carboxylate (compound No. S-6),

4-[(s)-1-Methylpropylcarbonyloxy]phenyl4"-decyloxy-3'-chlorobiphenyl-4'-carboxylate (compound No. S-7), and

4-[(s)-2-Methylbutylcarbonyloxy]phenyl 4"-decyloxy-3"-chlorobiphenylcarboxylate (compound No. S-8).

The phase transition temperatures of the compounds obtained in Examples1 and 2 and compounds Nos. S-3 to S-8 are shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Phase transition temperature of                                                ##STR14##                                                                    [compounds of formula (I) in which m is 1 and n is 0]                         Com-                                                                          pound                                                                         No.  R     X   Q*  C   Sx   Sc*  S.sub.A                                                                            N*   I                                  __________________________________________________________________________    S-3  n-C.sub.8 H.sub.17                                                                  3 F 2MB •81.9                                                                       •113.4                                                                       •135.0                                                                       •154.6                                                                       •164.0                                                                       •                            S-1  n-C.sub.10 H.sub.21                                                                 3 F 2MB •80.2                                                                       --   •153.6                                                                       •168.5                                                                       •171.8                                                                       •                            S-4  n-C.sub.12 H.sub.25                                                                 3 F 2MB •66.2                                                                       --   •154.0                                                                       •168.0                                                                       --   •                            S-5  n-C.sub.14 H.sub.29                                                                 3 F 2MB •70.0                                                                       •81.3                                                                        •141.4                                                                       •155.5                                                                       --   •                            S-6  n-C.sub.10 H.sub.21                                                                 3 F 1MP •61.4                                                                       --   •110.8                                                                       •157.4                                                                       --   •                            S-2  n-C.sub.12 H.sub.25                                                                 3 F 1MP •85.9                                                                       --   •144.3                                                                       •161.0                                                                       --   •                            S-7  n-C.sub.10 H.sub.21                                                                 3 Cl                                                                              1MP •26.6                                                                       --   (•12.9)                                                                      •33.7                                                                        --   •                            S-8  n-C.sub.12 H.sub.25                                                                 3 Cl                                                                              2MB •44.0                                                                       --   --   (•29.0)                                                                      (•42.9)                                                                      •                            __________________________________________________________________________

In column X of Table 1, 3F shows that the fluorine atom is substitutedat a position ortho to the alkoxy group of the biphenyl ring, and 3Cllikewise shows that the chlorine atom is substituted ortho to the alkoxygroup.

In Table 1, 2MB in the column of Q* represents an optically active2methylbutyl group, and 1MP represents an optically active1-methylpropyl group.

In the column of the phase transition temperature in Table 1, Crepresents a crystalline phase, S_(X), an undetermined smectic phase;S_(C) *, a chiral smectic phase; S_(A), a smectic A phase; N*, a chiralnematic phase; and I, an isotropic liquid. The point "." shows theexistence of the respective phase, and "-" shows the non-existence ofthe phase. The parenthesis shows that the phase is monotropic. Namely,that phase exists when the compound is overcooled. These abbreviationsused in Tables 2 to 6 below have the same meanings.

EXAMPLE 3 Synthesis of 4-[(s)-1-methylpropylcarbonyloxy]phenyl4'-decyloxy-3'-fluorobenzoate (compound No. S-9) [3-1] Synthesis of4-decyloxy-3-fluorobenzoic acid

To a flash containing 50 ml of chloroform was added 12.6 g of2-fluoroanisole, and 16.0 g of bromine was added dropwise over 1 hour at0° to 10° C. The mixture was stirred at the same temperature for 1 hour,and refluxed at 60° to 63° C. for 6 hours. After the reaction, thechloroform solution was washed with an aqueous solution of sodiumhydrogen sulfite, an aqueous solution of sodium bicarbonate, and water,and dried over anhydrous sodium sulfate. The chloroform was evaporatedto give 20.1 g of a crude product. The crude product was distilled underreduced pressure to give 16.2 g (yield 79%) of 4-bromo-2-fluoroanisole(95°-96° C./12 mmHg).

Subsequently, as in 1-3 above, the product was subjected to synthesis ofa Grignard reagent, blowing of carbon dioxide gas and acid treatment togive 3-fluoro4-methoxybenozic acid in a yield of 82%. The product wasthen subjected to demethylation and alkoxylation as in Example 1, [1-1]to give the desired product in a yield of 41% based on 2-fluoroanisole.

[3-2] Synthesis of 4-[(s)-1-methylpropylcarbonyloxy]phenyl4'-decycloxy-3'-fluorobenzoate

By the method shown in Example 1, [1-4], the desired product wasobtained in a yield of 82% as 4-decyloxy-3-fluorobenzoic acid from the4-decyloxy-3-fluorobenzoic acid synthesized in Example 3, [3-1] aboveand 4-hydroxyphenyl (s)-2-methylbutyrate of Example 2, [2-1].

NMR (CDCl₃), δ, (proton): 1.87-2.22 (28H); 2.33-2.70 (2H) multiplet;4.02-4.17 (2H) triplet; 6.90-7.99 (7H).

IR (cm⁻¹ cm), main absorptions; 2930, 2860, 1750, 1730, 1615, 1515,1305, 1190, 1075, 905, 755.

Mass Spectrum: M/e=486 (C.I. method).

Phase transition temperatures: I-S_(A) point=40.2° C., m.p.=34.4° C.

By the same reaction as in Example 3, the following compounds wereobtained.

4-[(s)-1-Methylpropylcarbonyloxy]phenyl 4'-dodecyloxy-3'-chlorobenzoate(compound No. S-10),

4-[(s)-2-Methylbutylcarbonyloxy]phenyl 4'-dodecyloxy-3'-chlorobenzoate(compound No. S-11),

4-[(s)-1-Methylpropylcarbonyloxy]phenyl 4'-decyloxy-2'-chlorobenzoate(compound No. S-12),

4-[(s)-2-Methylbutylcarbonyloxy]phenyl 4'-decyloxy-3'-fluorobenzoate(compound No. S13),

4-[(s)-2-Methylbutylcarbonyloxy]phenyl4'-tetradecyloxy-3'-fluorobenzoate (compound No. S-14), and

4-[(s)-1-Methylpropylcarbonyloxy]phenyl4'-tetradecyloxy-3'-fluorobenzoate (compound No. S-15).

The phase transition temperatures of the compound obtained in Examples 1and 2 and compounds Nos. S-10 to S-15 are shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________    Phase transition temperatures of                                               ##STR15##                                                                    [compounds of general formula (I) in which m = 0, n = 0, Y = H]               Com-                                                                          pound                                                                         No.  R     X   Q*  C   Sx Sc*  S.sub.A                                                                            N*   I                                    __________________________________________________________________________    S-10 n-C.sub.12 H.sub.25                                                                 3 Cl                                                                              1MP •48.6                                                                       -- (•14.8)                                                                      (•38.6)                                                                      --   •                              S-11 n-C.sub.12 H.sub.25                                                                 3 Cl                                                                              2MB •50.2                                                                       -- --   --   (•41.7)                                                                      •                              S-12 n-C.sub.10 H.sub.21                                                                 2 Cl                                                                              1MP •23.3                                                                       -- --   --   --   •                              S-13 n-C.sub.10 H.sub.21                                                                 3 F 2MB •48.1                                                                       -- --   --   •58.1                                                                        •                              S-9  n-C.sub.10 H.sub.21                                                                 3 F 1MP •34.4                                                                       -- --   •37.2                                                                        •40.2                                                                        •                              S-14 n-C.sub.14 H.sub.29                                                                 3 F 2MB •67.2                                                                       -- --   --   --   •                              S-15 n-C.sub.14 H.sub.29                                                                 3 F 1MP •54.9                                                                       -- --   --   --   •                              __________________________________________________________________________

As Referential Examples, the following nonhalogenated compounds weresynthesized and compared.

4-[(s)-2-Methylbutylcarbonyloxy]phenyl4"-octyloxybiphenyl-4'-carboxylate (compound No. R-1),

4-[(s)-2-Methylbutylcarbonyloxy]phenyl4"-decyloxybiphenyl-4'-carboxylate (compound No. R-2) ,

4-[(s)-2-Methylbutylcarbonyloxy]phenyl4"-dodecyloxybiphenyl-4'-carboxylate (compound No. R-3),

4-[(s)-1-Methylpropylcarbonyloxy]phenyl 4'-decyloxybenzoate (compoundNo. R-4), and

4-[(s)-1-methylpropylcarbonyloxy]phenyl 4'-dodecyloxybenzoate (compoundNo. R-5).

Table 3 shows the phase transition temperatures of compounds Nos. R-1 toR-5 above.

                                      TABLE 3                                     __________________________________________________________________________    Phase transition temperatures of                                               ##STR16##                                                                    [compounds of general formula (I) in which X = H, n = 0 and Y = H]            Com-                                                                          pound                                                                         No.  R     m  Q*  C    Sx   Sc*  S.sub.A                                                                            N*   I                                  __________________________________________________________________________    R-1  n-C.sub.8 H.sub.17                                                                  1  2MB •100.1                                                                       •103.4                                                                       •160.0                                                                       •188.6                                                                       •199.4                                                                       •                            R-2  n-C.sub.10 H.sub.21                                                                 1  2MB •97.1                                                                        --   •154.9                                                                       •180.1                                                                       •187.4                                                                       •                            R-3  n-C.sub.12 H.sub.25                                                                 1  2MB •99.2                                                                        •100.4                                                                       -    •173.6                                                                       •178.4                                                                       •                            R-4  n-C.sub.10 H.sub.21                                                                 0  1MP •40.8                                                                        --   (•35.5)                                                                      •53.7                                                                        --   •                            R-5  n-C.sub.12 H.sub.25                                                                 0  1MP •34.4                                                                        --   (•30.9)                                                                      •53.4                                                                        --   •                            __________________________________________________________________________

EXAMPLE 4 Synthesis of 4-[(s)-1-methylpropylcarbonyloxy]biphenyl4'-dodecyloxy-3'-fluorobenzoate (compound No. S-16) [4-1] Synthesis of4'-hydroxy-4-biphenyl (s)-2"-methylbutyrate

50.0 g of 4,4'-biphenol was dissolved in 200 ml of dry pyridine, and asolution of 12.5 g of (s)-2-methylbutyryl chloride in 50 ml of drymethylene chloride and 30 ml of dry pyridine was added dropwise at roomtemperature for about 1 hour with stirring. The mixture was furtherstirred at room temperature for 15 hours. Methylene chloride (400 ml)was further added, and the mixture was transferred to a separatoryfunnel. Dilute hydrochloric acid (300 ml) was added to the separatoryfunnel, and the mixture was vigorously stirred. The lower methylenechloride layer was separated, and the same operation was carried outtwice further. The product was washed with water until the washingbecame neutral. The methylene chloride layer was concentrated, and fromthe residue, 9.4 g of the desired 4'-hydroxy-4-biphenyl(s)-2"-methylbutyrate was obtained by silica gel column chromatographyusing hexane/ethyl acetate as an eluent. The yield of the product basedon (s)-2-methybutyryl chloride was 35%.

[4-2] Synthesis of 4-[(s)-1-methylpropylcarbonyloxy]-4'-biphenyl4"-dodecyloxy-3"-fluorobenzoate

In 10 ml of dry pyridine was dissolved 3.4 g of3-fluoro-4-dodecyloxybenzoyl chloride, and 2.7 g of4'-hydroxy-4-biphenyl (s)-2"-methylbutyrate produced in [4-1] above wasadded. The mixture was heated to form a solution. The solution was thenstirred at room temperature for 12 hours. The solution was then dilutedwith ethyl acetate, washed with a dilute aqueous hydrochloric acidsolution and washed with water. The ethyl acetate layer was concentratedto give crude crystals. The crude crystals were purified by silica gelcolumn chromatography using hexane/ethyl acetate. Recrystallization fromethanol to give 4.3 g (yield 75%) of the desired product.

NRM (CDCl₃), δ, (proton): 0.80-2.05 (32H) (methyl and methyleneprotons); 2.43-2.83 (1H) (methine proton); 4.03-4.18 (2H) (methyleneprotons): 6.92-8.05 (11H) (aromatic protons).

IR (KBr) (cm⁻¹), main absorptions: 2930, 2860, 1760, 1730, 1615, 1510,1270, 1210, 1170.

Mass spectrum: M/e=576 (C.I. method).

EXAMPLE 5 Synthesis of4-[(s)-2-methylbutylcarbonyloxy]-4'-biphenyl-4"-dodecyloxy-3"-fluorobenzoate(Compound No. SA-17) [5-1] Synthesis of4[(s)-2-methylbutylcarbonyloxy]-biphenyl-4'-ol

50.0 g of 4,4'-biphenol was dissolved in 250 ml of dry pyridine, and asolution of 13.5 g of (s)-3-methylbutanoyl chloride in 50 ml of drymethylene chloride and 30 ml of dry pyridine was added dropwise at roomtemperature over about 1 hour with stirring. Then, the mixture wasstirred at room temperature for 15 hours, and 400 ml of methylenechloride was added. The mixture was transferred to a separatory funnel.To the separatory funnel was added 300 ml of dilute hydrochloric acid,and the mixture was vigorously stirred. The lower methylene chloridelayer was separated, and the the same operation as above was carried outtwice. The methylene layer was then washed with water until the washingbecame neutral. The methylene chloride layer was concentrated, and fromthe residue, 9.8 g of 4-[(s)-2-methylbutylcarbonyloxy]-biphenyl-4'-olwas obtained by silica gel column chromatography using hexane/ethylacetate as an eluent. The yield was 35% based on (s)-3-methylbutanoylchloride.

[5-2] Synthesis of 4-[(s)-2-methylbutylcarbonyloxy]-biphenyl3'-fluoro-4'dodecyloxybenzoate

3.4 g of 3-fluoro-4-dodecyloxybenzoyl chloride was dissolved in 30 ml ofdry pyridine, and 2.9 g of4-[(s)-2-methylbutylcarbonyloxy]biphenyl-4"-ol produced in [5-1] wasadded. The mixture was heated to form a solution which was stirred atroom temperature for 16 hours. The solution was then diluted with ethylacetate, and washed with dilute hydrochloric acid and water. The ethylacetate layer was concentrated to obtain crude crystals. The crudecrystals were purified by silica gel column chromatography usinghexane/ethyl acetate as an eluent. Recrystallization from ethanol gave4.7 g (yield 80%) of the desired product.

NRM (CDCl₃), δ, (protons): 0.86-2.05 (32H) (methyl, methylene andmethine protons); 2.38-2.60 (2H) (methylene proton); 4.08-4.18 (2H)(methylene protons); 7.00-8.15 (17H) (aromatic protons).

IR (KBr) (cm⁻¹), main absorptions: 2940, 2870, 1755, 1730, 1615, 1500,1300, 1210, 1180.

Mass spectrum: M/e=590 (C.I. method).

EXAMPLE 6 Synthesis of4-[(s)-1-methylpropylcarbonyloxy]-3',3"-difluoro-4-biphenyl3"-fluoro-4"-dodecyloxybenzoate (compound No. S-18) [6-1] Synthesis of3,3'-difluoro-4,4'-dihydroxybiphenyl

Flaky metallic magnesium (2.43 g) was added to 50 ml of drytetrahydrofuran, and while the mixture was heated, a solution of 20.5 gof 4-bromo-2-fluoroanisole in 100 ml of dry tetrahydrofuran was addeddropwise little by little in a stream of nitrogen to prepare atetrahydrofuran solution of 3-fluoro-4-methoxy-phenyl magnesium bromide.Then, 18.0 g of 4-bromo-2-fluoroanisole was added to 100 ml of drytetrahydrofuran containing 0.05 g of iodine and 0.1 g of palladiumchloride. The mixture was maintained at 40° to 50° C. in a stream ofnitrogen, and the above-prepared tetrahydrofuran solution of3-fluoro-4-methoxyphenyl magnesium bromide was added dropwise gradually.The addition was completely in about 1 hour, and thereafter, the mixturewas reacted for 5 hours at the refluxing temperature of tetrahydrofuran.After the reaction, the reaction mixture was after-treated in acustomary manner to give 38.2 g of a crude product. The desired productwas isolated from the crude product by silica gel column chromatographyusing ethyl acetate/hexane as an eluent. Thus, 15.0 g of3,3'-difluoro-4,4'-dimethoxybiphenyl was obtained.

NMR (CDCl₃), δ, (proton): 3.89 (6H) (methyl protons); 6.86-7.31 (6H)(aromatic protons).

10.0 g of 3,3'-difluoro-4,4'-dimethoxybiphenyl was dissolved in 150 mlof dioxane, and 150 ml of 48% hydrobromic acid was added. The mixturewas heated under reflux for 50 hours. After the reaction, the reactionmixture was subjected to evaporation under reduced pressure. The residuewas fully washed with water to obtain the desired3,3'-difluoro-4,4'-dihydroxybiphenyl.

[6-2]

A solution of 12.0 g of (s)-2-methylbutyryl chloride in 100 ml of drymethylene chloride was added dropwise to a solution of 33.5 g of3,3'-difluoro-4,4'-dihydroxybiphenyl in 150 ml of dry pyridine at 0° to10° C. over 1 hour. Then, the mixture was stirred overnight at roomtemperature. The reaction mixture was diluted with 200 ml of methylenechloride, and washed several times with dilute hydrochloric acid andthen with water to give a methylene chloride solution containing thedesired product. The methylene chloride solution was concentrated, andfrom the residue, 15.1 g of the desired 3,3'-difluoro-4-hydroxybiphenyl(s)-2-methylbutyrate was obtained by silica gel column chromatographyusing hexane/ethyl acetate as an eluent.

NMR (CDCl₃), δ, (proton): 0.90-2.0 (8H) (methyl and methylene protons);2.55-2.85 (1H) (methine proton); 5.25 (1H) (hydroxyl proton); 6.89-7.50(6H) (aromatic protons).

[6-3] Synthesis of4-[(s)-1-methylpropylcarbonyloxy]-3,3"-difluorobiphenyl4"-dodecyloxy-3"-fluorobenzoate

3.41 g of 4-dodecyloxy-3-fluorobenzoyl chloride was dissolved in 20 mlof dry pyridine, and 3.09 g of 3,3'-difluoro-4"-hydroxybiphenyl(s)-2-methylbutyrate obtained from 3,3"-difluoro-4,4'-dihydroxybiphenylwas added. The mixture was heated at 50° to 60° C. to form a solution.The solution was stirred at the same temperature for 1 hour and then for20 hours at room temperature, then diluted with ethyl acetate, andwashed three times with dilute hydrochloric acid and then with water.The ethyl acetate layer was dried over anhydrous sodium sulfate, andconcentrated to obtain crude crystals. The crude crystals were purifiedby silica gel column chromatography using hexane/ethyl acetate as aneluent. Recrystallization from ethanol gave 5.0 g (yield 84%) of thedesired product.

NMR (CDCl₃), δ, (proton): 0.81-2.05 (31H) (methyl and methyleneprotons); 2.45-2.85 (1H) (methine proton); 3.96-4.10 (2H) (methyleneprotons); 6.93-8.05 (9H) (aromatic protons).

IR (KBr) (cm⁻¹), main absorptions: 2950, 2870, 1760, 1740, 1620, 1595,1515, 1400, 1340, 1300, 1195, 1130.

Mass spectrum: M/e=612 (C.I. method).

Phase transition temperature: N*-I point=114.8° C., S_(C) *-N*point=103.8° C., m.p.=67.8° C.

EXAMPLE 7 Synthesis of4-[(s)-2-methylbutylcarbonyloxy]-3,3'-difluorobiphenyl4"-dodecyloxybenzoate (compound No. S-19)

By carrying out the same reaction, after treatment and purification asin Example 6, [6-2] except that 13.5 g of (s)-3-methylpentanoyl chloridewas used instead of 12.0 g of (s)-2-methylbutyryl chloride, 16.2 g ofthe desired 3,3'-difluoro-4'-hydroxy-4-biphenyl(s) 3-methylpentanoatewas obtained.

NRM (CDCl₃), δ, (protons): 0.84-1.65 (8H) (methyl and methyleneprotons); 1.80-2.78 (3H) (methylene and methine protons); 5.30 (1H)(hydroxyl proton); 6.90-7.35 (6H) (aromatic protons).

Subsequently, 3.2 g of 4-dodecyloxybenzonyl chloride was dissolved in 20ml of dry pyridine, and 3.20 g of 3,3'-difluoro-4'-hydroxy-4-biphenyl(s)3-methylpentanoate was added. The mixture was heated to 50° to 60° C. toform a solution. The solution was stirred at the same temperature for 1hour and then at room temperature for 20 hours. The solution was thendiluted with ethyl acetate and washed with dilute hydrochloric acidthree times and then with water. The ethyl acetate layer wasconcentrated to obtain crude crystals. The crude crystals were purifiedby silica gel column chromatography using hexane/ethyl acetate as aneluent. Recrystallization from ethanol gave 4.82 g (yield 79%) of thedesired product.

NMR (CDCl₃), δ, (proton): 0.80≧2.0 (32H) (methyl, methylene and methineprotons); 2.50-2.80 (2H); 4.03-4.17 (2H) (methylene protons); 6.93-8.03(10H) (aromatic protons).

IR (KBr) (cm⁻¹), main absorptions: 2950, 2880, 1760, 1740, 1620, 1595,1515, 1300, 1195, 1130.

Mass spectrum: M/e=608 (C.I. method).

Phase transition temperatures: N*-I point=131.2° C., S_(C) *-N*point=114.0° C., m.p.=79.8° C.

In the same was as in Examples 4, 5, 6 and 7, the following compoundswere synthesized.

4'-[(s)-1-Methylpropylcarbonyloxy]-4-biphenyl3"-fluoro-4"-octyloxybenzoate (compound No. S-20),

4'-[(s)-1-Methylpropylcarbonyloxy]-4-biphenyl3"-fluoro-4"-decyloxybenzoate (compound No. S-21),

4'-[(s)-1-Methylpropylcarbonyloxy]-4-biphenyl3"-fluoro-4"-tetradecyloxybenzoate (compound No. S-22),

4'-[(s)-1-Methylpropylcarbonyloxy]-4-biphenyl3"-chloro-4"-dodecyloxybenzoate (compound No. S-23),

4'-[(s)-1-Methylpropylcarbonyloxy]-4-biphenyl2"-chloro-4"-decyloxybenzoate (compound No. S-24),

4'-[(s)-1-Methylpropylcarbonyloxy]-4-biphenyl2"-chloro-4"-tetradecyloxybenzoate (compound No. S-25),

4'-[(s)-2-Methylbutylcarbonyloxy]-4-biphenyl3"-fluoro-4"-octyloxybenzoate (compound No. S-26),

4'-[(s)-2-Methylbutylcarbonyloxy]-4-biphenyl3"-fluoro-4-decyloxybenzoate (compound No. S-27),

4'-[(s)-2-Methylbutylcarbonyloxy]-4-biphenyl3"-fluoro-4"-tetradecyloxybenzoate (compound No. S-28),

4'-[(s)-2-Methylbutylcarbonyloxy]-4-biphenyl3"-chloro-4"-dodecyloxybenzoate (compound No. S-29),

4'-[(s)-1-Methylpropylcarbonyloxy]-3,3'-difluoro-4-biphenyl3"-fluoro-4"-dodecyloxybenzoate (compound No. S-30),

4'-[(s)-1-Methylpropylcarbonyloxy]-3,3'-difluoro-4-biphenyl4"-decyloxybenzoate (compound No. S-31),

4'-[(s)-2-Methylbutylcarbonyloxy]-3,3'-difluoro-4-biphenyl4"-octyloxybenzoate (compound No. S-32),

4'-[(s)-2-Methylbutylcarbonyloxy]-3,3'-difluoro-4-biphenyl4"-decyloxybenzoate (compound No. S-33),

4'-[(s)-2-Methylbutylcarbonyloxy]-3,3'-difluoro-4-biphenyl4"-tetradecyloxybenzoate (compound No. S-34),

4'-[(s)-2-Methylbutylcarbonyloxy]-3,3'-difluoro-4-biphenyl3"-fluoro-4"-octyloxybenzoate (compound No. S-35),

4'-[(s)-2-Methylbutylcarbonyloxy]-3,3'-difluoro-4-biphenyl3"-fluoro-4"-decyloxybenzoate (compound No. S-36),

4'-[(s)-2-Methylbutylcarbonyloxy]-3,3'-difluoro-4-biphenyl3"-fluoro-4"-tetradecyloxybenzoate (compound No. S-37), and

4'-[(s)-2-Methylbutylcarbonyloxy]-3,3'-difluoro-4-biphenyl4"-dodecyloxy-3"-fluorobenzoate (compound No. S-38).

Table 4 shows the phase transition temperatures of compounds Nos. S-16to S-19.

                                      TABLE 4                                     __________________________________________________________________________    Phase transition temperatures of                                               ##STR17##                                                                    [compounds of general formula (I) in which m is 0 and n is 1]                 Com-                                                                          pound                                                                         No.  R     X   Y  Q*  C   Sx Sc*  N*   I                                      __________________________________________________________________________    S-20 n-C.sub.8 H.sub.17                                                                  3 F H  1MP •84.7                                                                       -- •140.3                                                                       •159.1                                                                       •                                S-21 n-C.sub.10 H.sub.21                                                                 3 F H  1MP •95.0                                                                       -- •141.5                                                                       •154.0                                                                       •                                S-16 n-C.sub.12 H.sub.25                                                                 3 F H  1MP •80.8                                                                       -- •141.2                                                                       •147.9                                                                       •                                S-22 n-C.sub.14 H.sub.29                                                                 3 F H  1MP •81.2                                                                       -- •140.3                                                                       •144.2                                                                       •                                S-23 n-C.sub.12 H.sub.25                                                                 3 Cl                                                                              H  1MP •72.7                                                                       -- • 120.4                                                                      •130.0                                                                       •                                S-24 n-C.sub.10 H.sub.21                                                                 2 Cl                                                                              H  1MP •68.8                                                                       -- --   •112.2                                                                       •                                S-25 n-C.sub.14 H.sub.21                                                                 2 Cl                                                                              H  1MP •57.4                                                                       -- --   •101.6                                                                       •                                S-26 n-C.sub.8 H.sub.17                                                                  3 F H  2MB •95.4                                                                       -- •150.3                                                                       •177.6                                                                       •                                S-27 n-C.sub.10 H.sub.21                                                                 3 F H  2MB •93.5                                                                       -- •151.5                                                                       •170.3                                                                       •                                S-17 n-C.sub.12 H.sub.25                                                                 3 F H  2MB •87.5                                                                       -- •151.5                                                                       •164.2                                                                       •                                S-28 n-C.sub.14 H.sub.29                                                                 3 F H  2MB •86.7                                                                       -- •146.1                                                                       •155.6                                                                       •                                S-29 n-C.sub.12 H.sub.25                                                                 3 Cl                                                                              H  2MB •85.4                                                                       -- •136.1                                                                       •149.6                                                                       •                                S-32 n-C.sub.8 H.sub.17                                                                  H   F  2MB •49.1                                                                       -- •93.2                                                                        •154.1                                                                       •                                S-33 n-C.sub.10 H.sub.21                                                                 H   F  2MB •59.9                                                                       -- •104.8                                                                       •149.0                                                                       •                                S-19 n-C.sub.12 H.sub.25                                                                 H   F  2MB •79.8                                                                       -- •114.0                                                                       •131.2                                                                       •                                S-34 n-C.sub.14 H.sub.29                                                                 H   F  2MB •76.3                                                                       -- •117.8                                                                       •137.3                                                                       •                                S-35 n-C.sub.8 H.sub.17                                                                  3 F F  2MB •76.3                                                                       -- •105.3                                                                       •139.4                                                                       •                                S-36 n-C.sub.10 H.sub.21                                                                 3 F F  2MB •78.6                                                                       -- •111.2                                                                       •135.3                                                                       •                                S-37 n-C.sub.12 H.sub.25                                                                 3 F F  2MB •79.8                                                                       -- •114.0                                                                       •131.2                                                                       •                                S-38 n-C.sub.14 H.sub.29                                                                 3 F F  2MB •83.8                                                                       -- •116.0                                                                       •127.8                                                                       •                                S-31 n-C.sub.10 H.sub.21                                                                 H   F  1MP •58.6                                                                       -- •102.6                                                                       •131.0                                                                       •                                S-30 n-C.sub.12 H.sub.25                                                                 H   F  1MP •64.7                                                                       -- •107.3                                                                       •127.1                                                                       •                                S-18 n-C.sub.12 H.sub.25                                                                 3 F F  1MP •67.8                                                                       -- •103.8                                                                       •114.8                                                                       •                                __________________________________________________________________________

As referential Examples for comparison, the compounds shown in Table 5were synthesized.

                  TABLE 5                                                         ______________________________________                                        Phase transition temperatures of                                               ##STR18##                                                                    Com-                                                                          pound                                                                         No.   R        Q*      C    Sx    Sc*   N*    I                               ______________________________________                                        R-6   n-C.sub.8 H.sub.17                                                                     1MP     •80.9                                                                        --    •137.3                                                                        •175.4                                                                        •                         R-7   n-C.sub.10 H.sub.21                                                                    1MP     •87.1                                                                        --    •143.9                                                                        •169.6                                                                        •                         R-8   n-C.sub.12 H.sub.25                                                                    1MP     •90.3                                                                        --    •147.3                                                                        •162.3                                                                        •                         R-9   n-C.sub.14 H.sub.29                                                                    1MP     •92.4                                                                        --    •148.3                                                                        •157.8                                                                        •                         R-10  n-C.sub.8 H.sub.17                                                                     2MB     •79.1                                                                        •81.8                                                                         •141.4                                                                        •191.0                                                                        •                         R-11  n-C.sub.10 H.sub.21                                                                    2MB     •87.2                                                                        •89.1                                                                         •149.8                                                                        •183.6                                                                        •                         R-12  n-C.sub.12 H.sub.25                                                                    2MB     •94.1                                                                        (•83.8)                                                                       •153.1                                                                        •175.9                                                                        •                         R-13  n-C.sub.14 H.sub.29                                                                    2MB     •96.4                                                                        (•95.9)                                                                       •154.6                                                                        •169.8                                                                        •                         ______________________________________                                    

EXAMPLE 8 Synthesis of4-[(s)-1-ethoxyethylcarbonyloxyphenyl]-4"-dodecyloxy-3"-fluorobiphenyl-4-carboxylate(compound No. S-39) [8-1] Synthesis of ethyl (s)-2-ethoxypropionate

A mixture of 20 g of (s)-(-)-ethyl lactate, 100 ml ofN,N'-dimethylformamide, 38 g of ethyl iodide and 30 g of silver oxidewas stirred at room temperature for 40 hours. The insoluble materialswere separated by filtration and water and hexane were added to thefiltrate to separate N,N'-dimethylformamide. The aqueous layer wassubsequently extracted twice with hexane, and the hexane layers weredried over anhydrous sodium sulfate. The product was distilled underreduced pressure to give 18.5 g of a fraction having a boiling point of86°-88° C./75 mmHg. Nuclear magnetic resoanance spectroscopy led to thedetermination that this fraction was the desired product.

NMR (CDCl₃), δ, (proton): 1.1-1.45 (9H) (methyl protons); 3.29-3.68 (2H)(ethoxy and methylene protons); 3.79-4.03 (1H) (methine proton);4.03-4.29 (2H) (ester and methylene protons).

[8-2] Synthesis of 4-hydroxyphenyl (s)-2-ethoxypropionate

9.0 g of the ethyl (s)-2-ethoxypropionate obtained in [8-1] was stirredfor 6 hours in 50 ml of a 5N aqueous solution of sodium hydroxide, andthen adjusted to pH 3 to 4 with dilute sulfuric acid under ice cooling.The resulting aqueous solution was extracted several times with ether.The ether layers were dried over anhydrous sodium sulfate, andconcentrated to obtain 5.6 g of (s)-2-ethoxypropionic acid. [α]_(D) ²⁰=-36.5 (c=0.2, chloroform).

NMR (CDCl₃), δ, (proton): 1.12-1.43 (6H) (methine protons); 3.30-3.70(2H) (ethoxy and methylene protons); 3.78-4.00 (1H) (methine proton).

5.6 g of the resulting (s)-2-ethoxypropionic acid was added to 10 ml ofthionyl chloride, and the mixture was refluxed for 5 hours. Thionylchloride was then evaporated under reduced pressure, and a solution of9.0 g of hydroquinone in 50 ml of dry pyridine was added, and themixture was stirred at 30° to 40° C. for 20 hours. The reaction mixturewas dissolved in a large amount of ethyl acetate, washed with dilutehydrochloric acid several times and then with water, and dried overanhydrous sodium sulfate. The ethyl acetate solution was concentratedand from the residue, 4.6 g of the desired oily product was obtained bysilica gel column chromatography using hexane/ethyl acetate as aneluent.

NMR (CDCl₃), δ, (protons): 1.15-1.30 (3H) (methyl protons); 1.49, 1.57(3H) (methyl protons) (doublet); 3.40-3.83 (2H) (methylene protons)3.97-4.28 (1H) (methine proton); 6.33 (1H) (hydroxyl proton); 6.92-7.14(4H) (aromatic protons).

[8-3] Synthesis of 4-[(s)-1-ethoxyethylcarbonyloxy]phenyl4"-dodecyloxy-3"-fluorobiphenyl-4'-carboxylate

Thionyl chloride (8.5 g) was added to 4.0 g of the4'-dodecyloxy-3'-fluorobiphenyl-4-carboxylic acid synthesized by themethod shown in Example 1, and one drop of pyridine was added. Themixture was refluxed for 6 hours. After the reaction, the reactionmixture was concentrated to obtain4'-dodecyloxy-3'-fluorobiphenyl-4-carbonyl chloride. To the product wasadded 2.15 g of 4-hydroxyphenyl (s)-2-ethoxypropionate. Furthermore, 10ml of dry pyridine was added, and the mixture was stirred at roomtemperature for 20 hours. After the reaction, the reaction mixture waspoured into a large amount of ethyl acetate, and the mixture was washedtwice with a dilute aqueous solution of hydrochloric acid, and threetimes with water. The ethyl acetate layer was dried over anhydroussodium sulfate, and concentrated to give 6.05 g of crude crystals. Thedesired product was separated by silica gel chromatography using ethylacetate/hexane as an eluent. Recrystallization from ethanol gave 4.01 g(yield 67%) of the desired product.

NMR (CDCl₃), δ, (protons): 0.80-2.0 (29H) (methyl and methyleneprotons); 4.38-4.82 (2H) (methylene proton) (ethoxypropionate portion):3.96-4.10 (2H) (methylene proton) (alkoxybiphenyl portion); 4.00-4.29(1H) (methine proton); 6.95-8.25 (11H) (aromatic protons).

Mass spectrum: M/e=592 (C.I. method).

Phase transition temperatures: S_(A) -I point=150.1° C., S_(C) *-S_(A)=121.0° C., m.p.=77.4° C.

In the same way as in Example 8, the following compounds weresynthesized.

4-[(s)-1-n-propoxyethylcarbonyloxy]phenyl4"-decyloxy-3"-fluorobiphenyl-4-carboxylate (compound No. S-40),

4-[(s)-1-ethoxyethylcarbonyloxy]phenyl4"-decyloxy-3"-fluorobiphenyl-4-carboxylate (compound No. S-41),

4-[(s)-1-n-propoxyethylcarbonyloxy]phenyl 3'-decyloxy-3'-fluorobenzoate(compound No. S-42),

4[(s)-1-n-octyloxyethylcarbonyloxy]phenyl4"-dodecyloxy-3"-fluorobiphenyl-4-carboxylate (compound No. S-43), and

4-[(s)-1-n-octyloxyethylcarbonyloxy]phenyl 3'-fluoro-4'-octyloxybenzoate(compound No. S-44).

For comparison, 4[(s)-1-ethoxyethylcarbonyloxy]phenyl4'-dodecyloxybenzoate was synthesized. (compound No. R-14).

The phase transition temperatures of these compounds are shown in Table6.

                  TABLE 6                                                         ______________________________________                                        Phase transition temperatures of                                               ##STR19##                                                                    (compounds of formula (I) in which n is 0, Y is                               H and Q* is 1-alkoxyethyl)                                                    Com-                                                                          pound                                                                         No.   R        m     X    Q*    C    Sc*   S.sub.A                                                                             I                            ______________________________________                                        S-41  n-C.sub.10 H.sub.21                                                                    1     3 F  1-EtO •86.5                                                                        •128.3                                                                        •158.5                                                                        •                      S-39  n-C.sub.12 H.sub.25                                                                    1     3 F  1-EtO •77.4                                                                        •121.0                                                                        •150.1                                                                        •                      S-40  n-C.sub.10 H.sub.21                                                                    1     3 F  1-PrO •68.4                                                                        •131.3                                                                        •148.8                                                                        •                      S-42  n-C.sub.10 H.sub.21                                                                    0     3 F  1-PrO •55.1                                                                        --    --    •                      S-43  n-C.sub.12 H.sub.25                                                                    1     3 F  1-Oct •78.6                                                                        •129.3                                                                        •133.9                                                                        •                      S-44  n-C.sub.8 H.sub.17                                                                     0     3 F  1-Oct •55.9                                                                        --    --    •                      R-14  n-C.sub.12 H.sub.25                                                                    0     H    1-EtO •43.7                                                                        --    •49.0                                                                         •                      ______________________________________                                    

In Table 6, 1-EtO represents an optically active 1-ethoxyethyl group;1-PrO, an optically active 1-propoxyethyl group, and 1-Oct, andoptically active 1-octyloxyethyl group.

EXAMPLE 9

Compound R-8 (m.p. 90.3° C.), compound S-16 (m.p. 80.8° C.) and compoundS-23 (m.p.72.7° C.) were mixed in amounts of 49 parts, 27 parts and 24parts, respectively. The resulting composition had a melting point of57.6° C. which is much lower than the melting point of compound R-8, andshowed a S_(C) * phase at a temperature in the range of 57.6° to 138.3°C.

EXAMPLE 10

Compound R-6 (m.p. 80.9° C.) and compound S-23 (m.p. 72.7° C.) weremixed in amounts of 49 parts and 51 parts respectively. The resultingcomposition was very difficult to crystallize and its melting pointcould not be measured. This composition showed a wide S_(C) * phase withthe upper limit of the S_(C) * phase temperature being 126.2° C.

EXAMPLE 11

Compound S-30, compound S-6 and compound R-5 were mixed in amounts of 30parts, 35 parts and 35 parts respectively. The resulting compositionshowed a S_(C) * phase at a temperature in the range of 19.1° to 89.5°C. (i.e., even in the room temperature range).

EXAMPLE 12

The spontaneous polarizations of compounds of formula (I) were measuredby the triangular wave method, and the results shown in the followingtable were obtained.

    ______________________________________                                                       Spontaneous                                                                              Measuring                                                          polarization                                                                             temperature                                         Compound No.   (nC/cm.sup.2)                                                                            (°C.)                                        ______________________________________                                        S-2            3.1        62                                                  S-4            1.0        64                                                  R-4            6.7        28                                                  R-5            5.7        29                                                  S-39           50.0       80                                                  S-40           130.0      68                                                  ______________________________________                                    

EXAMPLE 13

Compound S-4, compound S-1, compound S-6 and compound R-5 were mixed inamounts of 36 parts, 20 parts, 12 parts and 32 parts respectively. Themixture was heat-melted in a stream of nitrogen to form a uniformcomposition. This composition enantiotropically showed a S_(C) * phaseat a temperature of 34° to 110° C. (including temperature near roomtemperature).

A thin film cell was constructed by filling this liquid crystallinecomposition as an isotropic liquid two transparent glass electrodessubjected to rubbing alignment separated by a spacer having a thicknessof 2 micrometers. The cell was gradually cooled to obtain a chiralsmectic phase as a uniform monodomain. At 55° C., rectangular waves of100 Hz with a field strength of 20 V.p.p. were applied, and the lightswitching action was detected by a photomultiplier. Its response speedwas 400 microseconds. This led to the determination that the resultingcomposition can be a liquid crystal display element having a highresponse speed.

EXAMPLE 14

Fifty parts of compound S-23 and 50 parts of compound R-6 wereheat-melted in a stream of nitrogen to form a uniform liquid which wasfully shaken and stirred to form a composition. This composition had amelting point of 20° C. and showed a S_(C) * phase at temperatures up to126° C.

The composition was filled in a cell having a thickness of 2.2micrometers in the same way as in Example 13, and by applyingrectangular waves of 50 Hz and 20 V.p.p. at 50° C., its light switchingaction was detected. Its response speed was found to be 150microseconds. This led to the determination that the resultingcomposition can be a liquid crystal display element having excellentresponse characteristics.

EXAMPLE 15

Compound S-30, compound S-6 and compound R-5 were mixed in amounts of 45parts, 22 parts and 33 parts respectively as in Example 13 to form acomposition. The resulting composition showed a S_(C) * phase attemperatures of from 20° to 103° C.

As in Example 13, this composition was filled in a cell having athickness of 2.2 micrometers, and its light switching action wasdetected. With rectangular waves of 20 V.p.p. and 100 Hz, its responsespeed was as high as 166 microseconds. This led to the determinationthat the resulting composition can be used as a light switching element.

EXAMPLE 16

Compound S-39, compound S-41 and compound S-6 were mixed in amounts of28 parts, 12 parts and 60 parts respectively by the same operation as inExample 13 to form a composition which showed a S_(C) * phase at atemperature of from 64.1° to 136.6° C.

A cell was constructed as in Example 13 using this composition. At 75°C., rectangular waves of 20 V.p.p. and 100 Hz were applied, and itslight switching action was detected. Its response speed was found to beas high as 120 microseconds. This led to the determination that theresulting composition can be a liquid crystal display element havinghigh response.

EXAMPLE 17

Seventy parts of a pyrimidine-type smectic C composition (showing aS_(C) phase at 10° to 64° C.) was mixed with 30 parts of compound S-40as in Example 13 to form a uniform composition. This composition showeda S_(C) * phase at temperatures up to 93° C.

As in Example 13, the resulting composition was filled in a cell havinga thickness of 2 micrometers, and rectangular waves of 20 V.p.p. and 100Hz were applied. It was found that its response speed was 85microseconds at 50° C. and 93 microseconds at 25° C., showing excellentresults. This composition therefore had good temperaturecharacteristics. This led to the determination that the resultingcomposition can be an excellent light switching element.

What is claimed is:
 1. An optically active carboxylic acid derivativerepresented by the general formula ##STR20## wherein R represents anormal alkyl group having 5 to 20 carbon atoms, X represents a hydrogenor halogen atom, and Q* represents an optically active alkyl.
 2. Thecompound of claim 1, wherein R represents a linear alkyl group having 5to 18 carbon atoms.
 3. The compound of claim 1, wherein Q* represents anoptically active 1-methylpropyl group or an optically active2-methylbutyl group.